When an animal dies, a chain reaction of decomposition processes is set in motion. Until now, it was assumed that this reaction followed a largely fixed and therefore predictable pattern. In any case, forensic medicine relies on the organisms present on (or under) a corpse to provide clues as to how a person died.
However, wolf-killed ungulate carcasses do not follow a simple set of rules, a unique study by WSL researchers has found. The team led by Anita Risch, head of WSL's Plant-Animal Interactions research group, together with partners from the University of Minnesota, investigated the soil beneath carcasses in Yellowstone National Park in the United States.
Their paper, published in the journal Functional Ecology, reveals that very different bacteria and fungi thrive under a bison carcass compared with that of an elk. However, the microbial diversity beneath the carrion is less than that in the adjacent soil because specialised organisms dominate, displacing other microbes.
Rare nutrients beneath carcasses
Nevertheless, high concentrations of otherwise rare nutrients were found beneath the carcasses. These promote the growth of plants that are significantly more nutrient-rich than those found nearby. Such plants in turn attract herbivores, which are drawn to the high-quality food. "So you get this mosaic of hotspots in the landscape where the food supply is of above-average quality," says Risch.
Changes in the microbial communities over time could not be measured because, for safety reasons, the researchers were only able to visit carcasses that were over 40 days old. At more recent kills, the risk of encountering grizzly bears would have been too great.
According to Risch, this is the first large-scale study in the wild looking at the composition of microbial communities beneath carcasses. "The dead animals are rather like islands in the landscape, where nutrients are concentrated and soil biodiversity is modified," says Risch, who together with co-author Joseph Bump from the University of Minnesota examined a total of 19 wolf-killed carcasses in the national park.
The Yellowstone National Park offers a unique opportunity to investigate carcasses in a natural setting: the five wolf packs in the Northern Range (around 33 individuals) are fitted with satellite transmitters, ensuring that the location of their carrion is known. Moreover, the large size of elk and bison means that enough bones, gut contents and hair are left to enable the researchers to find the remains even 40 days after the kill.